Conventional methods, apparatus and systems are generally known in the art for providing mood or wash lighting in airplanes with an array of different colors and brightness levels. Conventional lighting apparatus use multiple single color Light Emitting Diodes (LEDs) to create these lighting effects.
There are a number of problems with such conventional methods, apparatus and systems. The mixing of the light from the separate red, green and blue LEDs is often incomplete and creates separate bands of color instead of the desired mixed color. Furthermore, current designs provide an inefficient use of aircraft space because, in order to create the desired colored lighting effects, the light from a relatively large number of separate red, green and blue LEDs must be combined. In addition, these conventional systems and apparatus use linear current sources that are pulse width modulated at low resolution to produce slow responding visible steps in brightness and imprecise color control when dimming. The use of these linear current sources with large voltage drops requires more power from the aircraft and creates a correspondingly large amount of heat that must be dissipated, thus, requiring large heat sinks.
In addition, conventional lighting apparatus operate in a relatively narrow voltage range. Thus, when the voltage supply in the aircraft drops, the lighting system and its lighting apparatus become unstable resulting in the LEDs flickering or turning off. Furthermore, conventional lighting apparatus use low resolution dimming schemes that limit the number of steps that can be taken to dim the light. This produces visual artifacts and loss of color control as the light nears its minimum dimming range. In a conventional lighting apparatus and system, 8-bit control is used thus limiting the total number of dimming steps, or levels, to 256. For example, to produce a certain color of amber at full brightness, the green LEDs are set to 250 and the red LEDs are set to 222. For this scheme, the ratio of the color level of green LEDs to red LEDs is 1.126:1. If the system is dimmed 50%, the green LEDs are now set to 125 and the red LEDs set to 111. The ratio is still 1.126:1. To maintain this ratio when the system is dimmed to 5% of the original brightness, the green LEDs would need to be set to 12.5 and the red LEDs set to 11.1. Instead, in conventional lighting systems using 8-bit control, the green LEDs are truncated to a color level of 12 and the red LEDs to a level of 11. The new ratio of 1.09:1 results in a noticeable difference in lighting color.
Calibration of light intensity to match batches of LEDs or to match aged LEDs with new replacement LEDs is a problem in conventional systems. It is typically achieved through a calibration divisor in the software that tends to reduce color resolution further. Even if a 10-bit system were used instead of an 8-bit system for the LED brightness, the use of such a calibration driver tends to drop the effectiveness of the 10-bit system to that of an 8-bit system when the new LEDs are much more efficient than the older LEDs to which they are being matched.
Current lighting system networks using RS485 require end of the line termination hardware so that reflections do not occur in the transmission line. Also, previous designs have used simple, direct protocol for communication. This creates bandwidth problems for high resolution systems that are too cost sensitive to use Ethernet or other such high speed networks.
Conventional systems are designed such that each individual LED limits at a predetermined level. When a low color temperature or monochromatic saturated color is produced, conventional systems simply produce less light instead of adjusting for the additional headroom of color available because of the substantially lower current draw.
A need exists for improved methods and apparatus to provide high resolution control for smooth dimming and precise control of color temperature.